This invention relates to a tilt shoe bearing and, in particular, to a bearing assembly which provides the individual shoes complete freedom to accommodate the shaft of a high-speed machine such as a turbine, compressor, or the like.
It is commonly known in the art that a tilt shoe bearing provides excellent hydrodynamic support to a rotor shaft when the shaft is turning at most shaft speeds. This type of bearing is most effective in reducing vibrations at speeds above the first critical shaft speed by stiffening the hydrodynamic fluid film maintained between the bearing and the shaft thus minimizing the effect of fluid film whirl. However, lightly loaded bearings operating below the first critical speed can experience fluid film instability which results in excessive vibrations. Similarly, tilt shoe bearings are known to experience other harmful effects, which are also associated with shaft speeds, leading to unwanted vibrations being set up in the system.
It has been long known that the effects of these harmful forces can be minimized or considerably reduced in a hydrodynamic or multiple shoe bearing assembly by allowing the individual shoes to adjust their relative positions in relation to the shaft when the shaft undergoes deflections or vibrations whereby an optimum fluid wedge is maintained between the shoes and the shaft. As exemplified in U.S. Pat. Nos. 3,022,123 and 3,297,371, it has been heretofore conventional in the art to pivotally mount each shoe in assembly to permit the shoe to roll in the direction of shaft rotation. Further means are also provided to enable the individual shoes to pitch in an axial direction while the shoe rolls in the direction of shaft rotation. Although these devices, which provide the individual shoes with two degrees of freedom, considerably reduce the adverse effects of load induced forces, it has nevertheless been found that a greater degree of freedom must be provided to the shoes to more efficiently dampen out the effects of shaft deflections and vibrations.